Bearing structure with reduced vibratory level for railroad track

ABSTRACT

A bearing structure for railroad track rails on a track bed, comprising several load distribution plates in a rigid material disposed side to side on the track bed, with each load distribution plate having a surface area and thickness predetermined in such a way that its first resonance frequency is greater than the first resonance frequency of the vibrations locally generated in the rails by the passage of the wheels of a vehicle on the rails. The different load distribution plates may advantageously be interconnected by joints allowing the pivoting of each load distribution plate with relation to adjacent load distribution plates. The load distribution plates may be placed on the ground of the track bed or on the foundation of a tunnel and they may also be integrated in the coating of a railroad way. The load distribution plates may bear rails of the railway track, switches and crossings, fixation systems on which the rails may be fixed or even ballast that itself bears cross ties on which the rails of the railway track are fixed.

TECHNOLOGICAL BACKGROUND

The present invention relates to bearing structures for railroad trackson a track bed.

A railroad track for a tramway, subway or train always generatesvibrations that propagate in and harm the environment. The vibratorylevels generated depend on the characteristics of the vehiclestransiting on the railroad track and the characteristics of the railroadtrack bed. For a standard ballasted track, the main frequency of thevibrations generated is approximately 60 Hz. This frequency isdetermined by the rigidity of the ballast and its under-layer, and bythe unsprung mass of the vehicle truck transiting on the railroad track.For a track placed directly on concrete, the main frequency of thevibrations generated is in a range from 40 to 60 Hz, depending on therigidity of the rail fixation system. This frequency is determined bythe rigidity of the rail fixation system and the concrete foundation andby the unsprung mass of the vehicle truck.

On the vibration propagation plane, it is found that a track placed on arigid soil (for example a rocky soil) results in vibratory levels withlower amplitudes than a track placed on a flexible soil (for example aclay soil). On the other hand, vibrations generated in rigid soilpropagate farther (they are less damped) than in flexible soil, which ismore shock absorbing.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a bearing structurefor railroad track rails that reduces significantly the vibratory levelgenerated by the passage of vehicle trucks transiting on the rails,whatever the road foundation of the railroad track bed. This object isreached according to the invention by a bearing structure for railroadtrack rails comprising several load distribution plates in a rigidmaterial, disposed side to side on the track bed, below the railroadtrack, each of these load distribution plates having a surface andthickness predetermined in such a way that its first resonance frequencyis greater than the first resonance frequency of the vibrations locallygenerated in the rails by the passage of vehicle trucks transiting onthe railroad track.

The aforementioned load distribution plates are relatively short, ratherthick plates that extend on the track bed, below the railroad track.They may be placed on the ground or integrated into the coating of atrain or tramway roadway and they may be placed on the foundation of asubway or train tunnel as well. The load distribution plates may be madeof concrete, a composite material, or another material capable ofdistributing the loads of vehicles intending to transit on the railroadtrack. They may be fabricated on site or may be prefabricated (modules)and they may be butt-jointed with joints that allow free rotation of aload distribution plate with relation to adjacent plates.

Thus, instead of exciting the ground very locally below a vehicle trucktransiting on the railroad track, the excitation is distributed over alarge surface (without dynamic amplification), with a resulting lowervibratory level. A vibration gain of at least 8 dB is obtained byutilizing such a load distribution plate over a non-rocky conventionalsoil. This vibratory level reduction is explained as follows: instead ofthe dynamic stresses of the four wheels of a truck being distributedover 4 m² (or 4 times 1 m²), here the stresses are distributed over asurface of at least 10 m² (by considering a load distribution plate thatis 4 m long and 2.5 m wide), which gives a vibratory amplitude reductionfactor of 2.5 (or approximately 8 dB). This dynamic stress distributionresults in a vibratory level of the ground below this load distributionplate that is markedly less than that which would be produced withoutthis load distribution plate.

Each load distribution plate is dimensioned such that its firstresonance frequency is greater than approximately 1.4 times the firstresonance frequency of vibrations locally generated in the rails by thepassage of a vehicle over the railroad track rails. In the case wherethis first resonance frequency of locally generated vibrations is 57 Hz,for example, the first resonance frequency of the load distributionplate must be greater than 80 Hz. Therefore, when a vehicle passes onthe railroad track above a load distribution plate, the plate isdeformed in conformance with its static deformation without significantdynamic amplifications due to the resonances. In the example citedabove, to arrive at a first resonance frequency of the load distributionplate that is greater than 80 Hz having a concrete slab with a length of4 m (and not wider than 4 m), it must have a thickness of at least 400mm.

Each load distribution plate in the bearing structure according to theinvention may be made in the form of a single beam or any other suitableform provided that it has a first resonance frequency (torsion orflexion) greater than the first resonance frequency of the vibrationslocally generated by the passage of a vehicle transiting on the rails ofthe railroad track. The load distribution plates may be utilized undernormal tracks (in alignment and in curves), under switches and crossingsor under ballast.

Other details and special features of the invention will be apparentfrom the following description and the attached drawings, whichillustrate examples of embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a longitudinal section in a railroad track bearingstructure according to the invention, with ballast;

FIG. 2 is a plan view showing the load distribution plates of FIG. 1;

FIG. 3 shows a longitudinal section in a railroad track bearingstructure according to the invention for fixing rails on concreteblocks;

FIG. 4 is a plan view of the railroad track bearing structure from FIG.3;

FIG. 5 shows a plan view of a railroad track bearing structure accordingto the invention for integrating rails in concrete load distributionplates;

FIG. 6 is a plan view according to line A-A of FIG. 5;

FIG. 7 illustrates several possible cross sections for the loaddistribution plates.

In these drawings, the same reference numerals identify identical orequivalent elements in the bearing structure.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

By referring to FIGS. 1 and 2, an example of a railroad track bearingstructure according to the invention with ballast may be seen. Therailroad track bearing structure, designated in its entirety by thereference 10, comprises cross ties 11 on which the rails (notrepresented) are fixed in the usual manner, and ballast 12. Inconformance with the invention, a set of dynamically rigid loaddistribution plates 13 extend below the ballast, which plates themselvesrest on the ground of the track bed 14. The load distribution plates 13are relatively short, rather thick plates, that are disposed end-to-endon the ground, below the ballast. They may advantageously bebutt-jointed with joints that allow the free rotation of a plate withrelation to adjacent plates. Each load distribution plate 13 has asurface and thickness predetermined in such a way as to present a firstresonance frequency that is greater than the first resonance frequencyof the wheel/rail system. This latter resonance frequency is determinedby the rigidity of the ballast and by the unsprung mass of the vehicletruck transiting on the railroad track. In general, the first resonancefrequency of the vibrations locally generated by the passage of avehicle transiting on the railroad track is below 80 Hz.

To be effective, each load distribution plate must have a firstresonance frequency greater than approximately 1.4 times the firstresonance frequency of the vibrations locally generated in the rails bythe passage of a vehicle transiting over the railroad track. In the casewhere this first resonance frequency of locally generated vibrations is57 Hz, for example, the first resonance frequency of the loaddistribution plates must be greater than 80 Hz. Therefore, when avehicle passes on the railroad track above a load distribution plate,the latter is deformed in conformance with its static deformation,without significant dynamic amplifications due to the resonances. Toarrive at a first resonance frequency of the load distribution plategreater than 80 Hz with a concrete slab of 4 m long (and not wider than4 m), for example, each load distribution plate must have a thickness ofat least 400 mm.

With the bearing structure of the invention, the dynamic stressesgenerated by the passage of four wheels of a truck over a section oftrack are thus distributed over the surface of the load distributionplate situated below said track section instead of the stresses beingapplied very locally (4 times 1 m²) on the ground. The result is a lowervibratory level exciting the ground. By utilizing a load distributionplate 13 with a surface of at least 10 m² (by considering a loaddistribution plate that is 4 m long and 2.5 m wide) over a conventionalnon-rocky soil, the vibratory amplitude applied to the soil is reducedby a factor of 2.5 (or approximately 8 dB).

The load distribution plates 13 may be made of concrete, a compositematerial or other material capable of distributing the loads of vehiclesintending to transit on the railroad track. They may be fabricated onsite or may be prefabricated (modules).

In the railroad track bearing structure according to the invention, theload distribution plates 13 may also be provided for the direct fixationof rails on concrete through any rail fixation system (discrete orcontinuous).

FIGS. 3 and 4 illustrate an example of embodiment of the invention inwhich the load distribution plates 13 are provided for the directfixation of rails by means of discrete rail fixation systems 15 that arefixed on the load distribution plates 13. In this embodiment too, theload distribution plates 13 are relatively short, rather thick platesdisposed end-to-end on the ground 14 and they may be connected by jointsthat allow the free rotation of a plate with relation to adjacentplates. Also, they may be fabricated on site or may be prefabricated(modules) and they may be integrated in the roadway pavement.

FIGS. 5 and 6 represent an embodiment of the railroad track bearingstructure according to the invention in which the relatively short,rather thick load distribution plates 13 disposed end-to-end on theground 14 comprise grooves 13A in which the rails (not represented) maybe integrated. Also, the load distribution plates may be connected byjoints that allow the free rotation of a plate with relation to adjacentplates. Such load distribution plates may be fabricated on site or maybe prefabricated (modules) and they may be integrated in the roadwaypavement.

The railroad track bearing structures according to the invention may beutilized under normal tracks (in alignment and in curves) and underswitches and crossings as well.

As indicated above for the case of a ballasted track, each loaddistribution plate must have a surface and thickness predetermined insuch a way that its first resonance frequency is greater than 1.4 timesthe first resonance frequency of the vibrations locally generated in therails by the transit of a vehicle on the railroad track. The resultingbehavior of the load distribution plates and the reduction in vibratoryamplitude are the same as in the case of a ballasted track.

Each load distribution plate may be made in the form of a single beam asillustrated in FIG. 7A or any other suitable form provided that it has afirst resonance frequency greater than the first resonance frequency ofthe vibrations locally generated in the rails by the transit of avehicle on the railroad track, as indicated above. FIGS. 7B to 7Dillustrate some examples of cross sections for load distribution plates13. FIG. 7B shows a section comprising a bearing plate 13 with lateralsides 13B which extend to the bottom of the bearing plate. FIG. 7C showsa section that differs from that of FIG. 7B by the presence of alongitudinal rib 13C. Several ribs may also be provided. FIG. 7D shows asection in which plate 13 comprises grooves 13A intended to receive therails of the railroad track.

1. A bearing structure for railroad track rails on a track bed,comprising several load distribution plates in a rigid material disposedside by side on the track bed, under the railroad track, each loaddistribution plate having a surface area and thickness predetermined insuch a way that its first resonance frequency is greater than the firstresonance frequency of the vibrations locally generated in the rails bythe passage of the wheels of a vehicle transiting on the rails.
 2. Therailroad track rail bearing structure as claimed in claim 1, in whichthe load distribution plates are interconnected by joints allowingpivoting of each load distribution plate with relation to adjacent loaddistribution plates.
 3. The railroad track rail bearing structure asclaimed in claim 1, in which each load distribution plate has its firstresonance frequency greater than 1.4 times the first resonance frequencyof the vibrations locally generated in the rails by the passage of thewheels of a vehicle transiting on the rails.
 4. The railroad track railbearing structure as claimed in claim 1, in which each load distributionplate is placed on the ground of the track bed.
 5. The railroad trackrail bearing structure as claimed in claim 1, in which each loaddistribution plate is placed on the foundation of a tunnel.
 6. Therailroad track rail bearing structure as claimed in claim 1, in whicheach load distribution plate is integrated in the roadway pavement. 7.The railroad track rail bearing structure as claimed in claim 1, inwhich at least one load distribution plate is placed under switches andcrossings.
 8. The railroad track rail bearing structure as claimed inclaim 1, in which each load distribution plate comprises grooves toreceive the rails of the railroad track.
 9. The railroad track railbearing structure as claimed in claim 1, in which at least one loaddistribution plate bears ballast that itself bears cross ties on whichthe rails are fixed.
 10. The railroad track rail bearing structure asclaimed in claim 1, in which at least one load distribution plate bearsfixation systems on which the rails are fixed.
 11. The railroad trackrail bearing structure as claimed in claim 1, in which each loaddistribution plate is made in the form of a beam.
 12. The railroad trackrail bearing structure as claimed in claim 1, in which at least one loaddistribution plate comprises lateral sides extending to the bottom ofthe plate.
 13. The railroad track rail bearing structure as claimed inclaim 11, in which at least one load distribution plate furthermorecomprises at least one longitudinal rib.
 14. The railroad track railbearing structure as claimed in claim 12, in which at least one loaddistribution plate furthermore comprises at least one longitudinal rib.